The present invention relates to liquid crystalline polyesters resulting from the use of 4,4'-bis(p-carboxyphenoxy)biphenyl or 4,4'-bis(p-carboxyphenoxy)diphenyl ether. These dicarboxyphenylethers which are obtained from the nitrodisplacement of alkyl nitrobenzoate with the appropriate biphenols can be used in the synthesis of several liquid crystalline polyesters.
Prior to the present invention, aromatic thermotropic liquid crystalline polymers had received considerable attention in the chemical literature as shown by "Polymeric Liquid Crystals", A. Blumstein, Ed. Plenum Press, New York (1985), and U.S. Pats. such as U.S. Pat. Nos. 4,522,974, 4,496,712, and 4,374,228. It was generally known that repeating units, such as 1,4-phenylene and 4,4'-biphenylene, impart valuable properties to polyesters, such as high tensile strength and heat and chemical resistance. However, many of these liquid crystalline polyesters have limited commercial utility, because their T.sub.m 's are greater than 375.degree. C. Various flexible spacers, such as methylene units, oxymethylene groups and siloxane groups have been used in the polymer backbone to reduce the melt temperature of the polymer.
The present invention is based on a discovery that a flexible spacer having the formula, ##STR1## where X is selected from a C.sub.(6-) arylene radical or a C.sub.( 6-14) aryleneoxyarylene radical, can be incorporated into a polyester backbone to form a polyester exhibiting anisotropic properties in the melt at temperatures in the range of from about 175.degree. C. to 290.degree. C.